Add gnosis/dex E2E target

[cgewecke]

Description

Adds gnosis/dex-react as an E2E test target. This repo is a good sanity check that Web3 works with:

• react
• webpack production build
• real-world typescript compilation

Also re-wrote the yarn resolutions helper script so it's generic and will coerce Web3 to the appropriate version for any project which has Web3 in it's sub-dependency tree.

Initial commit added a log line in web3-eth-contract's constructor to verify that CI is actually installing the current Web3 state in the target and its code is getting run. The output should be visible at the links below.

• gnosis/dex proof
• mosaic proof

[EDIT - actually you have to click into the job and scroll down the output to see it...]

Fixes #3529

Type of change

• Test

Checklist:

• I have selected the correct base branch.
• I have performed a self-review of my own code.
• I have commented my code, particularly in hard-to-understand areas.
• I have made corresponding changes to the documentation.
• My changes generate no new warnings.
• Any dependent changes have been merged and published in downstream modules.
• I ran npm run dtslint with success and extended the tests and types if necessary.
• I ran npm run test:unit with success.
• I ran npm run test:cov and my test cases cover all the lines and branches of the added code.
• I ran npm run build-all and tested the resulting files from dist folder in a browser.
• I have updated the CHANGELOG.md file in the root folder.
• I have tested my code on the live network.
• The browser visual inspection check looks ok: sudden-playground.surge.sh

[coveralls]

Coverage remained the same at 89.833% when pulling 4cf3c72 on issue/3529 into ee1b56b on 1.x.

[ryanio]

nice, this LGTM! Tests: 176 passed, 176 total

I will add this as a required check.